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In the electron beam device, the cathode provides electrons with the initial energy. According to its emission mechanism, the electron source includes thermal cathode, cold cathodes, etc. With the cold cathode, the power consumption of the cathode is decreased. The delay time of the electron emission after the applying of voltage is very small in a device with a cold cathode. However, the perpendicular energy distribution of the electrons emitted from the cold cathode is a little larger than that of the thermionic cathode. An additional focusing structure has to be designed if the cold cathode is applied in the RF amplifier. In cathode ray tube and the field emission display panel, the electron current emitted from the cathode has to be modulated. Because of the high electric field in front of the cold cathode, the swing of the voltage for the current modulation is a little high. In this paper, an insulator tunnel is adopted in a cold cathode. When the primary electron bombarded on the surface of the insulator tunnel, the secondary electrons are generated. This paper studies the characteristic of the cold cathode with the secondary electron emission. The structure of the insulator tunnel is designed. As results, the perpendicular energy distribution of the electrons has been decreased effectively. Because the initial energy of the secondary electron is often smaller than that of the primary electron, the driving voltage for the current modulation is also decreased after the introduction of the insulator tunnel.